This invention relates to rotary drum vacuum filters in which the drum surface is divided into individual elongated sectors each of which is provided with lead and trail outlets.
More specifically, the invention is directed to an improved drum construction and piping arrangement for such a filter.
It is a common filtration practice to equip a drum filter with so-called lead and trail outlets for more efficient removal of filtrate and wash liquids. Also, it is known to arrange the valve operation to conduct a so-called purge or sweep in which prior to cake discharge pressured air enters through ports on the trailing side of the sector and is withdrawn through the ports in the descending side of the sector.
In the usual drum, each filtrate outlet port of a sector connects to the filter valve through its own internal pipe. The result is a complex plurality of internal pipes that terminate in ports in a trunnion which register successively with appropriate zones of the filter valve. As is well known, the valve connects through a vacuum receiver to a vacuum pump. The valve may also have a vent to atmosphere and/or a connection to pressured gas or liquid. With appropriate settings, the valve sequentially applies vacuum to the sectors for cake formation, washing and drying. It may also be set to release vacuum and supply pressured gas to the sector as an aid in cake discharge.
In large filters, many outlets are required hence the piping becomes complicated and costly to install and maintain. In addition, the internal piping system limits the hydraulic capacity of the filter. Another problem in large filters is the need for extra structural members to insure physical integrity of the drum.